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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Stable CW Single-Frequency Operation of Fabry-Perot Laser Diodes by Self-Injection Phase Locking

Previously, single-frequency semiconductor laser operation using fiber Bragg gratings has been achieved by two methods: 1) use of the FBG as the output coupler for an anti-reflection-coated semiconductor gain element'; 2) pulsed operation of a gain-switched Fabry-Perot laser diode with FBG-optical and RF-electrical feedback. Here, we demonstrate CW single frequency operation from a non-AR coated Fabry-Perot laser diode using only FBG optical feedback. We coupled a nominal 935 run-wavelength Fabry-Perot laser diode to an ultra narrow band (18 pm) FBG. When tuned by varying its temperature, the laser wavelength is pulled toward the centerline of the Bragg grating, and the spectrum of the laser output is seen to fall into three discrete stability regimes as measured by the side-mode suppression ratio.

Duerksen, Gary L.↗
NASA NTRS1999

Stable CW Single Frequency Operation of Fabry-Perot Laser Diodes by Self-Injection Phase Locking

Previously, single-frequency semiconductor laser operation using fiber Bragg gratings has been achieved by tWo methods: 1) use of the FBG as the output coupler for an anti-reflection-coated semiconductor gain element'; 2) pulsed operation of a gain-switched Fabry-Perot laser diode with FBG-optical and RF-electrical feedback'. Here, we demonstrate CW single frequency operation from a non-AR coated Fabry-Perot laser diode using only FBG optical feedback.

Duerksen, Gary L.↗
NASA NTRS2006

Interrupt-based Phase-locked Frequency Multiplier

A method aud system utilize a processor's digital timer and two interrupts to form a frequency multiplier. The first internipt's processing time window is definable by a first uumber of counts C(sub 1), of the digital timer while the second interrupt's processing time window is definable by a second number of counts C(sub 2) of the digital timer. A count value CV utilized by the systedmethod is based on a desired frequency multiplier N(sub 1), the timer clock rate, and the tiole required for one cycle of an input signal. The first interrupt is triggered upon completion of one cycle ofthe input sigual at which point the processing time window associated therewith begins. The second interrupt is triggered each time the timer's overflow signal is generated at which point the processing time window associated with the second interrupt begins. During the occurrence of the second interrupt's processing. the count value CV is modified to maintain the first interrupt's processing time window approximately centered between two of the second internipt's processing time windows.

Palumbo, Daniel L.↗
NASA NTRS2005

Frequency and Phase-lock Control of a 3 THz Quantum Cascade Laser

We have locked the frequency of a 3 THz quantum cascade laser (QCL) to that of a far-infrared gas laser with a tunable microwave offset frequency. The locked QCL line shape is essentially Gaussian, with linewidths of 65 and 141 kHz at the -3 and -10 dB levels, respectively. The lock condition can be maintained indefinitely, without requiring temperature or bias current regulation of the QCL other than that provided by the lock error signal. The result demonstrates that a terahertz QCL can be frequency controlled with l-part-in-lO(exp 8) accuracy, which is a factor of 100 better than that needed for a local oscillator in a heterodyne receiver for atmospheric and astronomic spectroscopy.

Betz, A. L.↗
DOE OSTI2021

Evolution of Charge-Lattice Dynamics across the Kuramoto Synchronization Phase Diagram of Quantum Tunneling Polarons in Cuprate Superconductors

Because of its sensitivity to the instantaneous structure factor, S(Q,t = 0), Extended X-ray Absorption Fine Structure (EXAFS) is a powerful tool for probing the dynamic structure of condensed matter systems in which the charge and lattice dynamics are coupled. When applied to hole-doped cuprate superconductors, EXAFS has revealed the presence of internal quantum tunneling polarons (IQTPs). An IQTP arises in EXAFS as a two-site distribution for certain Cu–O pairs, which is also duplicated in inelastic scattering but not observed in standard diffraction measurements. The Cu–Sr pair distribution has been found to be highly anharmonic and strongly correlated to both the IQTPs and to superconductivity, as, for example, in YSr 2 Cu 2.75 Mo 0.25 O 7.54 (T c =84 K). In order to describe such nontrivial, anharmonic charge-lattice dynamics, we have proposed a model Hamiltonian for a prototype six-atom cluster, in which two Cu-apical-O IQTPs are charge-transfer bridged through Cu atoms by an O atom in the CuO 2 plane and are anharmonically coupled via a Sr atom. By applying an exact diagonalization procedure to this cluster, we have verified that our model indeed produces an intricate interplay between charge and lattice dynamics. Then, by using the Kuramoto model for the synchronization of coupled quantum oscillators, we have found a first-order phase transition for the IQTPs into a synchronized, phase-locked phase. Most importantly, we have shown that this transition results specifically from the anharmonicity. Finally, we have provided a phase diagram showing the onset of the phase-locking of IQTPs as a function of the charge-lattice and anharmonic couplings in our model. We have found that the charge, initially confined to the apical oxygens, is partially pumped into the CuO 2 plane in the synchronized phase, which suggests a possible connection between the synchronized dynamic structure and high-temperature superconductivity (HTSC) in doped cuprates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1994

Hydrogen-Maser/Ruby-Maser/Quartz-Crystal Oscillator

Highly stable oscillator suitable for use as 100-MHz frequency standard consists of 100-MHz hydrogen maser combined with double-phase-locked-loop receiver. Generates 100-MHz signal with reduced noise. Contains 100-MHz voltage-controlled quartz-crystal oscillator (VCO) locked in phase to superconducting-cavity maser oscillator (SCMO). SCMO, locks in phase to hydrogen maser, phase-locking receiver and its SCMO/ VCO combination to hydrogen maser. Aspects of SCMO described in previous reports, including "Performance of Superconducting-Cavity Maser" (NPO-18175), NASA Tech Briefs, Vol. 15, No. 6. Performances of component oscillators complement each other.

Wang, Rabi T.↗
DOE OSTI2024

Shapiro steps and stability of skyrmions interacting with alternating anisotropy under the influence of ac and dc drives

Here we use atomistic simulations to examine the sliding dynamics of a skyrmion in a two-dimensional system containing a periodic one-dimensional stripe pattern of variations between low and high values of the perpendicular magnetic anisotropy. The skyrmion changes in size as it crosses the interface between two anisotropy regions. On applying combined dc and ac driving in either parallel or perpendicular directions, we observe a wide variety of Shapiro steps, Shapiro spikes, and phase-locking phenomena. The phase-locked orbits have two-dimensional dynamics due to the gyrotropic or Magnus dynamics of the skyrmions and are distinct from the phase-locked orbits found for strictly overdamped systems. Along a given Shapiro step when the ac drive is perpendicular to the dc drive, the velocity parallel to the ac drive is locked while the velocity in the perpendicular direction increases with increasing drive to form Shapiro spikes. At the transition between adjacent Shapiro steps, the parallel velocity jumps up to the next step value, and the perpendicular velocity drops. The skyrmion Hall angle shows a series of spikes as a function of increasing dc drive, where the jumps correspond to the transition between different phase-locked steps. At high drives, the Shapiro steps and Shapiro spikes are lost. When both the ac and dc drives are parallel to the stripe periodicity direction, Shapiro steps appear, while if the dc drive is parallel to the stripe periodicity direction and the ac drive is perpendicular to the stripe periodicity, then there are only two locked phases, and the skyrmion motion consists of a combination of sliding along the interfaces between the two anisotropy values and jumping across the interfaces.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Phase and Frequency Locked Magnetron

Phase and Frequency locked magnetrons have many important uses from phased array ground penetrating radars to SRF sources. We report on the recent progress in making such a magnetron. The ferrite/garnet material has passed bakeout and outgassi ng tests with outgassing rates well below the requirements. The magnetic field requirements for adjusting the frequency by changing the microwave properties of the ferrite/garnet have been determined. The design of the anode structure with ferrites, magne tic shielding, and magnetic bias has been completed for a low power test. We report on the design status. Muons, Inc. has negotiated an contract with a manufacturing firm, L-3 Electron Devices California Tube Laboratory, Inc., to be the Manufacturing Part ner for the commercialization of this technology and support these Phase II efforts.

43 PARTICLE ACCELERATORS↗
NASA NTRS1980

Torque control for electric motors

Method for adjusting electric-motor torque output to accomodate various loads utilizes phase-lock loop to control relay connected to starting circuit. As load is imposed, motor slows down, and phase lock is lost. Phase-lock signal triggers relay to power starting coil and generate additional torque. Once phase lock is recoverd, relay restores starting circuit to its normal operating mode.

Bernard, C. A.↗
NASA NTRS1973

Code regenerative clean-up loop transponder for a mu-type ranging system

A loop transponder for regenerating the code of a mu type ranging system is disclosed. It includes a phase locked loop, a code generator, and a loop detector. The function of the phase locked loop is to provide phase lock between a received component wk of the range signal and a replica rafter wk of the received component, provided by the code generator. The code generator also provides a replica of the next component rafter w(w+1). The loop detector responds to wk rafler wk and rafter w(k+1) to determine when the next component w(k+1) is received and controls the code generator to supply w(k+1) to the phase locked loop and to generate a replica rafter w(k+2) of the next component.

Hurd, W. J.↗